1. Field of the Invention
In common use in the dental profession are three way syringes for discharging pressurized air and water flows into the mouth. Such devices typically include a discharge nozzle which is detachable because of the necessity to sterilize or replace it before use with a new patient. Commonly, the nozzle is replaced after each use, because of the expense and difficulty of sterilization.
The nozzle commonly consists of an inner tube and a concentric outer tube. The present invention relates to the retention of the inner tube within the outer tube. This retention is necessary to maintain the separation of air and water as they flow from the syringe head into the passageways in the discharge nozzle. The separation of air and water is important for dental procedures which require air, but during which no water can be present. The retention of the inner tube also helps to ensure a mist when the practitioner desires both air and water.
The invention also relates to the prevention of media blockage as media flows into the nozzle.
2. Description of the Prior Art
As shown in U.S. Pat. Nos. 4,248,589; 5,242,300; 5,342,195; and 5,433,485; commonly, dental syringes utilize an O-ring to maintain separation of air and water. This 0-ring can fail to maintain separation of air and water if the nozzle is not completely inserted into the syringe, or if the inner tube is not retained at a predetermined placement within the outer tube.
U.S. Pat. Nos. 4,248,589; and 5,433,485 retain the inner tube, but in so doing close off the air passageway, and therefore utilize a groove about the outer tube and a new hole in the side of the outer tube. This increases manufacturing costs and the retail price, and therefore decreases the likelihood that the practitioner will replace the nozzle after a single use. U.S. Pat. No. 5,433,485 provides for an indicium with the intent that it will be obscured when the nozzle is properly inserted into the syringe. However, if the nozzle is used with the syringes of other manufacturers, the indicium may not be located at the appropriate location in relation to the various syringes.
U.S. Pat. No. 5,342,195; in the embodiment shown in FIGS. 10-11, requires a press fit of the two components, which would tend to increase manufacturing costs.
U.S. Pat. No. 5,242,300 utilizes an oblique end face at the proximal end of the outer tube to prevent media blockage. An oblique end face would be very difficult to chamfer, which decreases the likelihood that it will be utilized in manufacture.